Select Menu

Select All

Selects the whole layer. Shortcut Ctrl + A

Deselect

Deselects everything (except for active Selection Mask). Shortcut Ctrl + Shift + A

Reselect

Reselects the previously deselected selection. Shortcut Ctrl + Shift + D

Invert Selection

Inverts the selection. Shortcut Ctrl + Shift + I

Convert to Vector Selection

This converts a raster selection to a vector selection. Any layers of transparency there might have been are removed.

Convert to Raster Selection

This converts a vector selection to a raster selection.

Convert Shapes to Vector Selection

Convert vector shape to vector selection.

Convert to Shape

Converts vector selection to vector shape.

Display Selection

Display the selection. If turned off selections will be invisible. Shortcut Ctrl + H

Show Global Selection Mask

Shows the global selection as a selection mask in the layers docker. This is necessary to be able to select it for painting on.

Scale...

Scale the selection.

Select from Color Range...

Select from a certain color range.

Select Opaque

Select all opaque (non-transparent) pixels in the current active layer. If there's already a selection, this will add the new selection to the old one, allowing you to select the opaque pixels of multiple layers into one selection. Semi-transparent (or semi-opaque) pixels will be semi-selected.

Feather Selection...

Feathering in design means to soften sharp borders. So this adds a soft border to the existing selection. Shortcut Shift + F6

Grow Selection...

Make the selection a few pixels bigger.

Shrink Selection...

Make the selection a few pixels smaller.

Border Selection...

Take the current selection and remove the insides so you only have a border selected.

Smooth

Make the selection a little smoother. This removes jiggle.